Audio Spectrum Analyzer - Real-Time FFT from Your Mic

A spectrum analyzer turns sound into a picture: the horizontal axis is frequency, the vertical axis is level, and every vertical bar shows how much energy your microphone is picking up in one narrow frequency band. Under the hood, an AnalyserNode runs a Fast Fourier Transform (FFT) on the incoming audio many times per second. The FFT size you choose sets the fundamental trade-off of all spectral analysis: a larger FFT divides the spectrum into finer slices (better frequency resolution) but needs a longer stretch of audio per frame (worse time resolution). At a 48,000 Hz sample rate, a 2,048-point FFT resolves about 23.4 Hz per bin and reacts within roughly 43 ms, while an 8,192-point FFT sharpens resolution to about 5.9 Hz per bin at the cost of a 171 ms window that smears fast transients. Pick small for drums and speech, large for tuning and bass work. What can you actually do with it? Room acoustics is the classic use: play a song or pink noise through your speakers and watch the spectrum. A stubborn mountain in the 40 to 120 Hz region that grows in corners is a room mode — standing waves set by your room's dimensions — and moving the speakers or the listening position visibly flattens it. Live engineers use analyzers for feedback hunting: when a PA starts to ring, the feedback frequency shows up as a thin, steadily climbing spike, and the peak readout hands you the number to pull down on a graphic EQ before the squeal takes over. Musicians can read harmonics directly. Play a single guitar note and you will see the fundamental plus a ladder of overtones at integer multiples — an A at 110 Hz puts spikes near 220, 330, and 440 Hz — which is a great way to understand timbre, spot fret buzz energy, or check that a piano string's partials are where they should be. The peak readout converts the strongest frequency into the nearest equal-tempered note with its offset in cents, so the analyzer doubles as a rough chromatic tuner for whistling, singing, and sustained instruments. The Freeze button holds the current frame so you can inspect a moment without the display dancing away, and the analyzer applies modest smoothing between frames so the bars are readable rather than frantic. Audio processing such as echo cancellation and noise suppression is disabled on the microphone stream, since those helpers deliberately reshape the spectrum you are trying to observe. Everything runs locally in your browser — the microphone signal is analyzed in memory and never recorded, stored, or transmitted.